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Several years ago I installed slate tiles on my steps at the front of my house
(outdoor). I installed them on a wood base built from pressure treated lumber
and plywood. The decking and treads are built up from two layers of glued and
screwed pressure treated plywood. The tiles are set in a thinset mortar
purchased from the tile supplier. The mortar is a modified mix which is
supposed to be appropriate for the job. I mixed in some latex additive to
enhance the bond. The tiles are set in mortar that has been applied with a 1/2
inch notched trowel and the tiles are back buttered. After grouting the step
was sealed with latex sealer.
The problem is that the tiles pop loose after about two years and have to be
reinstalled. This year I removed almost 80% of the tiles and have noted that
the steps leading up to the deck were starting to rot. I have removed the steps
and need to rebuild. When I removed the tiles I noted that the mortar was not
adhered to the tile or the step and I simply swept the mortar off with a broom.
At this point I am not sure whether to put the tiles back on or go to something
more durable like exposed aggregate. I am thinking that I should try something
like removing the plywood and replacing it with a cementitous product like
wonderboard. Alternatively, I could try securing metal lath to the existing
deck and applying the mortar to it.
Some timely advice would be greatly appreciated. I like the look of the tile
much more than going to concrete but its been a total pain in the neck.
Replies
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Good evening Murray,
Just two little questions for now.
You wouldn't be located in a region that experiences freeze thaw cycles, would ya?
Or you wouldn't be located in a region that has serious heat for long periods of time, would ya?
Those are about the only two things that will totally destroy thinset.
Gabe
*Try glue, honest. Construction adhesive will bind to the tiles like you wouldn't believe. I currently like the OSI subfloor adhesive; I don't know if there is much difference brand-to-brand. the rot is different, that is a failure of your assembly to exclude and/or release moisture.
*Totally unqualified opinion/question: That I can think of, I have never seen a masonry product applied over wood in an exterior application. Seems very odd to me, and it seems that the fact that the wood is exposed to moisture, and therefore constantly swelling and contracting, would make the two materials incompatible. Also, isn't the masonry products being in direct contact with the wood what is causing the wood to rot? Am I missing something here?
*I, too, think tile on wood is asking for problems. Concrete backer board, screwed to the wood, would help. Keep the thin-set moist as long as you can after installation so it develops its full strength. Pre-wet the tile backs and the backer board. Work on a humid day. Stiffen the steps if there is ANY flex in them.Or go with an adhesive as suggested above. -David
*A caveat -- we installed the tile on a sheltered porch, so it is exposed to temperature flux but not much water. The plywood is pressure-treated, and I will likely leave the bottom exposed to give it more air.Isn't slate a bit slippery for steps?
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Thanks for all of the advice. I thought I should answer some of the questions put forward in the discussion.
To Gabe; I live in Canada, central Alberta to be exact, and we do experience sever temperature swings. However, every masonry tradesman I speak to insists that the tile should stick. On the deck there were about 5 square feet of mortar and tile that were secure. This area is close to the house in a corner.
To Andrew; Do you have a specific brand or type of construction adhesive that you would recommend. Will the OSI sublfoor adhesive bond to pressure treated plywood? Also, the entire deck is covered with an overhanging roof. The only water that reaches the deck is blown in. Yes the slate is a little slippery when we get a lot of rain but the area I live in does not experience major rainfall. In the winter the steps have good traction. I have never had anyone slip on the steps or deck.
To Matt; The only place I was experiencing rot was in the step and it was mostly underneath the step, not where the masonry was in contact with the wood. I think that because the step and deck are built between the house and a brick planter there is no opportunity for moisture to escape. I am thinking that I need to provide some ventilation to allow any built up moisture to escape. At this time I am looking at providing a continuous vent about 1 inch wide at the top of each riser.
To Dave; I think you are correct and I will secure wonderboard to the decking before installing the tile. To try to prevent water ingress I am going to seal the joints and edges before laying the tile. The steps and deck are both very stiff and have little to no flex. To help counteract any flex I will use latex additive in the mortar mix and perhaps prepare the surface with a wash of the same material.
Again, thanks for all the input. I am always open to more advice and will try to post my final solution.
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Murray, I used PL const adhesive all winter but got tired of its "oozing" problem in hot weather (it keeps coming out of the tube after you put the gun down, apparently because of trapped air). I just pulled up some boards glued with the OSI adhesive -- yes, pt -- and the wood failed before the adhesive did. $3 for 30 oz. You should explore use of these polyurethane adhesives in general. just don't use Liquid Nails, it is inferior and usually more $$$.
The cementious backer boards, as I understood it, was really for ceramic tile, to provide an even and attractive substrate for the thinset. But I don't mean to say there's anything wrong with using the thinset! The glue is just quick and easy, and it never become entirely hard which I suspect might help with your popping problem. Plus you can NOT remove the glue from the tile without solvent or destroying the tile. Read < Obsolete Link > this discussion from earlier on this board -- Rich knows a lot about this stuff.
*Sorry for the late reply but I agree with not applying tiles directly over wood. Cment board is probably good as may be some wire mesh to the wood first then the mortar over that but at any rate the wood expands at a different rate than does concrete and will therefore never prove top be longlasting in any of the above suggestions although some will last longer than others. There is a product for tile to wood applications called koroseal i believe it remains pliable but holds like the dickens for wood to ceramic or natural stone. I would tend to worry that the non-pourus, slick surface of slate may be troublesome too.One more point is that the treating solution on PT wood may lessen the effectiveness of the bond of your adhesive to the wood. Try a naturally weather resistant wood or maybe just let the PT lumber age the 6 mos as recommendedPete
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Several years ago I installed slate tiles on my steps at the front of my house
(outdoor). I installed them on a wood base built from pressure treated lumber
and plywood. The decking and treads are built up from two layers of glued and
screwed pressure treated plywood. The tiles are set in a thinset mortar
purchased from the tile supplier. The mortar is a modified mix which is
supposed to be appropriate for the job. I mixed in some latex additive to
enhance the bond. The tiles are set in mortar that has been applied with a 1/2
inch notched trowel and the tiles are back buttered. After grouting the step
was sealed with latex sealer.
The problem is that the tiles pop loose after about two years and have to be
reinstalled. This year I removed almost 80% of the tiles and have noted that
the steps leading up to the deck were starting to rot. I have removed the steps
and need to rebuild. When I removed the tiles I noted that the mortar was not
adhered to the tile or the step and I simply swept the mortar off with a broom.
At this point I am not sure whether to put the tiles back on or go to something
more durable like exposed aggregate. I am thinking that I should try something
like removing the plywood and replacing it with a cementitous product like
wonderboard. Alternatively, I could try securing metal lath to the existing
deck and applying the mortar to it.
Some timely advice would be greatly appreciated. I like the look of the tile
much more than going to concrete but its been a total pain in the neck.